This invention relates to elastomer compositions and methods of making elastomer compositions. More particularly it relates to elastomer-thermoplastic compositions and methods of making elastomer-thermoplastic compositions.
Often a single material cannot provide all the properties which are desired of an article of manufacture. Thus, a single chemical substance will not provide an article that simultaneously has high strength and rubber elasticity, or high hardness and stiffness, on the one hand, and high traction on the other.
When confronted by a challenge of this type, frequently the solution is to combine two materials in order to provide a new material with the requisite characteristics. Previously elastomers (rubbers) have been used in combination with thermoplastics to provide composites with elasticity and high strength. All approaches to date involve layers of the two different materials with the layers adhered to each other either by adhesive or by surface bonding.
For example. U.S. Pat. No. 4.835,063 to Jadamuss et al. discloses composite parts comprising a layer of thermoplastic which contains polyphenylene ether surrounded by a layer of styrene-butadiene rubber (SBR) or of styrene-butadiene-styrene (SBS) which is in turn, surrounded by a layer of natural rubber.
There can be an optional intermediate layer comprising a mixture of powdered SBR and filler between the SBR layer and the natural rubber layer.
U.S. Pat. No. 5,153,076 to Jadamus et al. discloses a method of chemically bonding polyphenylene ether containing material and synthetic rubber by covulcanization. The chemical bond is between the surfaces of the two materials and is achieved by contacting the two materials and subjecting them both to vulcanization conditions.
U.S. Pat. No. 5,332,621 to Schmidt et al. discloses a composite article comprising latex foam intimately bonded to a thermoplastic molded part containing polyphenylene ether. Once again the elastomeric material and the thermoplastic material are present in discrete layers.
As is clearly seen from the above patents, the approach to date for combining elastomers and thermoplastics has focused on composite materials comprised of layers of each material that are surface bonded to each other. This is due to the substantial differences in processability as well as the limited compatibility of poly(arylene ether) and rubber. The layered composite approaches do not provide a uniform property profile throughout the material which limits the applicability of these materials in situations, such as tire treads, where elasticity and high strength are important, especially at elevated temperatures.
There is an ongoing effort to improve the materials used in tire treads. Key issues are wear resistance, wet grip (traction) and rolling resistance. A tire tread with excellent properties in all three areas will be long wearing and will improve both safety and fuel economy. It is commonly believed that a higher glass transition temperature (Tg) corresponds to an improved wet grip and wear resistance although it can also result in increased rolling resistance. Tan delta (tan xcex4), the viscoelastic loss factor (the internal friction) of a material as measured with dynamical mechanical testers, at low temperatures (typically 0xc2x0 C.) should be high to improve wet grip. Tan xcex4 at high temperatures (typically 75-80xc2x0 C.) should be low to improve rolling resistance. Current tread materials have tans values ranging from 0.16 to 0.20 at 75xc2x0 C.
Accordingly, there remains a need in the art for elastomer-thermoplastic compositions with elasticity and high strength, especially at elevated temperatures, and methods of making them.
The above described drawbacks and disadvantages are overcome by an elastomer-thermoplastic composition and a method for making the same. The composition comprises: styrene butadiene random copolymer and poly(arylene ether) resin. Meanwhile, the method comprises combining styrene butadiene random copolymer and poly(arylene ether) in a solvent to form an emulsion, solution or suspension; and evaporating the solvent.